Fuel cells have been proposed as a power source for automotive vehicles and other applications. One type of fuel cell is the proton exchange membrane (PEM) fuel cell that includes a membrane-electrode-assembly (MEA) comprising a thin, solid polymer membrane electrolyte having an anode on one face and a cathode on the opposite face. The anode and cathode typically comprise finely divided carbon particles, very finely divided catalytic particles supported on the internal and external surfaces of the carbon particles, and proton conductive material intermingled with the catalytic and carbon particles. The MEA is sandwiched between a pair of electrically-conductive contact elements that serve as current collectors for the anode and cathode and that contain appropriate flow channels and openings (“flow field”) for distributing the fuel cell's gaseous reactants (H2 or other gaseous fuel supplied to the anode and O2/air or other oxidizing gas supplied to the cathode) over the surfaces of the anode and cathode. In the case of hydrogen as the fuel and oxygen as the oxidizing gas, water is generated at the cathode from the oxidation of the hydrogen fuel.
PEM fuel cells comprise a plurality of the MEAs stacked together in electrical series while being separated one from the next by an impermeable, electrically-conductive contact element known as a bipolar plate or septum. The bipolar plate has two working surfaces, one confronting the anode of one cell and the other confronting the cathode on an adjacent cell in the stack, to conduct electrical current between the adjacent cells. The bipolar plate is formed with flow fields on its working surfaces for gas distribution. The bipolar plate may be made of an electrically conductive, polymeric composite, for example a polymer/graphite composite such as a vinyl ester polymer and conductive powder, e.g., graphite powder, combination. Composite bipolar plates may offer advantages, such as low weight and ease of manufacture because flow fields may be molded in when the plate is formed rather than being engraved into the surface as with metal bipolar plates. Molding the bipolar plate from a composite material, however, produces a polymer-rich outer skin on the molded part that must be removed so as not to interfere with the electroconductivity of the bipolar plate. The skin must be removed in a way that avoids damaging the thin, lightweight bipolar plate.